Recently, it has become more important to sense, detect, or determine the quantity of biological materials such as DNAs, enzymes, antigens, antibodies, protein, viruses or cells or chemical materials in the field of medical treatment, health, foods and drug development or the like, and various biochips and micro chemical chips (hereinafter collectively referred to as “microchips”) have been proposed which can measure the biological materials easily.
With the microchip, a series of examination and analysis operations conventionally performed in laboratories may be performed in the small chip. Thus, on-chip detection has many advantages in that the examination and analysis may be performed with a small amount of specimen and liquid reagent, but at low cost, with a fast reaction rate, and high throughput, and results of the examination and analysis may be obtained immediately when the specimen is collected.
In the related art, a microchip is known, which includes a plurality of portions (chambers) for carrying out specific treatments for liquid such as a specimen or liquid reagent present in the so-called fluid circuit (or a micro fluid circuit) and a flow path network consisting of fine flow paths which connect the portions properly. In the examination or analysis on the specimen using the microchip having therein such a fluid circuit, various processes such as measuring the specimen introduced into the fluid circuit (or specific component in the specimen) or liquid reagents to be mixed therewith (by moving them to a measuring portion for performing the measuring), mixing the specimen (or a specific component in the specimen) with the liquid reagent (by moving them to a mixing portion for performing the mixing) portion, and moving the specimen or the liquid reagent from one portion to another portion are performed.
In addition, hereinafter, “fluid treatment” refers to a process performed for various liquids (such as the specimen, the specific component in the specimen, the liquid reagent, or a mixture of two or more thereof) in the microchip. These various fluid treatments can be performed by applying centrifugal force in an appropriate direction with respect to the microchip.
In order to perform a good control of the fluid treatment in the microchip, it is important to ensure the liquid in the fluid circuit is moved from one portion to another portion along a path as intended (as designed) when the centrifugal force is applied in a predetermined direction. If at least a portion of the liquid is not moved to a predetermined portion, thereby departing from the intended path, and moved elsewhere in the fluid circuit, a predetermined fluid treatment may not be properly performed. Thus, it is likely that the accuracy in the examination and analysis on the specimen is lowered or the examination and analysis itself may not be performed.
One of major factors which would cause the liquid in the fluid circuit to depart from the intended path at the application of the centrifugal force is a high wettability of the liquid with respect to an inner surface of the fluid circuit. When the liquid in the fluid circuit has a high wettability with respect to the inner surface of the fluid circuit, the liquid may be moved along an unintended path on account of the action of force causing the liquid to move along the side surface of the fluid circuit due to the high wettability, even though the centrifugal force is applied in a predetermined direction so as to move the liquid along the predetermined path.
In order to solve the problem as described above, a technique is known in the related art which reduces the wettability of the liquid with respect to the inner surface of the fluid circuit by applying a water-repellent agent on the inner surface of the fluid circuit. However, the method complicates a manufacturing process of the microchip, thus reducing production efficiency significantly. In addition, it is difficult to control the wettability of the liquid with respect to the inner surface for only a portion of the fluid circuit.